As a film deposition method in a semiconductor manufacturing process, there has been known a method for depositing a film on a substrate, which makes, under vacuum atmosphere, a semiconductor wafer (hereinafter referred to as “wafer”), which is a substrate, adsorb a first process gas (material gas) on its surface, then switches a gas to be supplied from the first process gas to a second process gas (reaction gas) so as to form one or more atomic layers and molecular layers by the reaction of the first and second gases, and repeats this cycle plural times so as to stack these layers. This film deposition method, which is referred to as, e.g., an ALD (Atomic Layer Deposition) method or an MLD (Molecular Layer Deposition) method, can precisely control a film thickness depending on the number of cycles, and can provide an excellent film quality, i.e., a high in-plane uniformity. Thus, such a film deposition method is an effective method capable of coping with a thinner film of a semiconductor device.
For example, JP2004-6733 A (particularly paragraph 0056 and FIG. 8) describes a film deposition apparatus for carrying out this film deposition method, wherein a film is deposited on a surface of a substrate placed in a process container (vacuum container) by alternately flowing two kinds of process gases from a left side surface of the process container to a right side surface thereof (or from the right side surface to the left side surface). When there is employed such a side flow method in which a process gas is flown from one side to the other side of a substrate, lateral non-uniformity of a film thickness and of a film quality can be restrained. Thus, such a film deposition process can be performed under a relatively low temperature atmosphere such as about 200° C.
For example, when a high dielectric constant material such as zirconium oxide (ZrO2) is deposited, a TEMAZ (tetrakis ethyl methyl amino zirconium) gas is used as the first process gas (material gas), and an ozone gas is used as the second process gas (reaction gas). Since a decomposition temperature of the TEMAZ gas is high, a film deposition process is performed at a temperature as high as, e.g., 280° C. However, under this high temperature condition, since a reaction speed is also high, a film thickness of a film deposited during one cycle tends to be thicker. In particular, in the side flow method, since a moving distance of a gas on the surface of the substrate is long, there is a possibility that a film thickness might be large on a gas supply side, but might be small on an exhaust side. In this case, an excellent in-plane uniformity of the film thickness cannot be obtained.
In addition, when a supply time of an ozone gas as a reaction gas is reduced in order to improve a throughput, for example, an oxidation ability of the ozone gas becomes weaker at a point more distant from a supply source of the ozone gas (ozone gas is consumed). Thus, there is a possibility that the high dielectric constant material adsorbed on the substrate might not be oxidized in a sufficiently uniform manner. In this case, values of leak currents of semiconductor devices formed in the wafer may be deviated.
In order to solve the above disadvantage of the side flow method, the following method is under review. Namely, by using a gas showerhead (see JP2006-299294A (particularly paragraphs 0021 to 0026)) for use in a general CVD apparatus, for example, a process gas is supplied from above a central part of a substrate, and a non-reacted process gas and a reaction byproduct are discharged from a bottom part of a process container. In this type of gas supply-and-discharge method, the process gas to be supplied flows from the center of the substrate toward a periphery thereof. Thus, a moving distance of the gas becomes shorter than that in the side flow method, so that a high in-plane uniformity of a film thickness and of a film quality of the deposited film can be expected after the film deposition.
It has been found that, in order to perform a satisfactory film deposition process by the above type of method that supplies a process gas with the use of the showerhead, it is advantageous that the substrate and the showerhead are close to each other, so as to make narrow a process atmosphere space between the substrate and the showerhead. However, when the substrate is brought excessively close to the showerhead, there is not left enough room in which the substrate is transferred between an external transfer mechanism and a stage on which the substrate is to be placed.
Further, when a transfer opening is formed on a lateral side of the process atmosphere in a sidewall of the process vessel, the atmosphere surrounding the substrate is made asymmetric in the in-plane direction of the substrate, when viewed from the center of the process atmosphere. This inhibits the in-plane uniformity of the process. Thus, the transfer opening should be formed at a position lower than the process atmosphere. In order therefor, the process container is required to have a sufficient height allowing that the stage is moved upward and downward between a position at which the substrate is processed and a position at which the substrate is transferred.
Furthermore, in order that a reactant such as a reaction product and a reaction byproduct does not deposit on an inner wall of the process container, it is necessary to heat an area thereof, with which the process gas comes into contact, to a temperature (evaporation temperature of the reactant) higher than a temperature allowing adhesion of the reactant. Generally, in a process container of a single-wafer type for a CVD process, an inner wall of the process container is heated at a temperature of 200° C. at most. However, when a high dielectric constant material such as Zr oxide and St oxide is used, a temperature allowing evaporation of the reactant is much higher. Thus, an area of the process container ranging from a portion of the sidewall near to the process atmosphere to the bottom wall, including the transfer opening below the portion of the sidewall, should be heated to, e.g., about 280° C.
However, when the entire process container is heated to such a high temperature, a grease of a drive system for moving the stage upward and downward, a grease of another drive system for driving a gate valve of the transfer opening though which a substrate is loaded, and an O-ring, which is a sealing member made of a resin, for hermetically closing the process container, are deteriorated. In addition, since a heat resistance of a commercially available manometer is about 200° C. at most, it becomes difficult to measure a pressure in the process container. Moreover, the enlarged size of the process container for securing a space required for the vertical movement of the stage is disadvantageous in that a larger amount of energy is necessary for heating the entire process container to such a high temperature.